1. Field of the Invention
The present invention relates to a marker (also called a tag or a label) for use in a magnetic electronic article surveillance system (EAS), the marker being of the type having an elongated alarm strip composed of an amorphous ferromagnetic alloy and at least one activation strip composed of a semi-hard magnetic alloy.
2. Description of the Prior Art
Magnetic antitheft systems and markers are well known and have been described in detail, for example, in European Application-0 121 649 and in PCT Application WO 90/03652. On the one hand, there are magnetoelastic systems in which the activation strip serves to activate the alarm strip by magnetization and, on the other hand, there are harmonic systems in which the activation strip serves, after its magnetization, to deactivate the alarm strip.
The alloys with semihard magnetic properties which are used for premagnetization strips include Co--Fe--V alloys, which are known as Vicalloy, Co--Fe--Ni alloys, which are known as Vacozet, and Fe--Co--Cr alloys. These known semihard magnetic alloys contain high proportions of cobalt, in some cases of at least 45% by weight, and are correspondingly expensive. In addition, these alloys are brittle in the magnetically final-annealed state, so that they do not have sufficient ductility to meet sufficiently the requirements for the display elements for antitheft systems. It is in fact a requirement for the display elements in magnetic antitheft systems that they have to be insensitive to bending and deformation.
In addition, the approach now being adopted is to introduce the display elements of antitheft systems directly into the product to be protected (source tagging). As a result, there is additionally the need to be able to magnetize the semihard magnetic alloys even from a relatively large distance or with relatively small fields. It has become apparent that the coercive force has to be restricted to values of 60 A/cm at maximum.
On the other hand, however, sufficient opposing field stability, as a result of which the lower limit of the coercive force is defined, is also required. Only coercive forces of at least 30 A/cm are suitable for this.